Apparatus for measuring the concentration of vitamin a



. Dec. 9,1941.

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' Zmi;" ';;33%% m RNEY KIFAECIUP B. DEMAREST 2,265,357

APPARATUS FOR MEASURING THE CONCENTRATION- OFVI'I'AVMIN A Filed July 18,1940 arrears 3r awn-cw Z3 smu 1941 APPARATUS FOR MEASURING THE CON-CENTRATION OF VITAMIN A Beaumont Demarest, Englewood, N. 1., assignor toNational Oil Products Company, Harrison,

' N. 1., a corporation of New Jersey Application July 18, 1940, SerialNo. 346,097

4Ciaims.

This invention relates to measuring apparatus and in one of itsmorespecific aspects it is directed to an improved apparatus for measuringthe concentration of vitamin A.

The apparatus embodying my invention has, among others, the followingcharacteristics. When compared with spectrophotometers used formeasuring the concentration oif vitamin A, the apparatus embodying my'invention will be found to be less expensive to produce, more convenientand easier to operate, eliminates bias of the observer or operator andtime saving. In addition, when compared with any photoelectric vitamin Aapparatus known, the apparatus embo'dying the invention will be foundsuperior in precision. These as well as other advantages of theinvention will be readily apparent from the following description anddrawing, wherein:

Figure 1 represents a atic sketch of the apparatus embodying myinvention.

Figure 2 is a curve showing the absorption characteristics of vitamin Afor various radiation between 2600 and 4000 Angstrom units.

As shown in the drawing, the invention comprises a photoelectric cellhaving an anode l0 and a cathode ll composed of a photosensitivematerial, such as sodium, which is non-responsive to visible light ofwave lengths above about 5000 Angstrom units. A source of electric enery, which may be a plurality of dry cells l2 connected in series, has theend negative pole thereof connected to the cathode II by conductor l3andhas the end positive pole thereof connected to a movable switchcontact l4 by conductor l5.

A stationary contact it of said switch is connected to one side of acondenser l1 by conductor l8 and theother side of condenser I1 isconnected to the anode l0by conductor I 9. A high resistance "has oneend thereof connected to conductor I! and its other end connected to aresistance 2| by conductor 22. The resistance of element 20 may be aboutohms. The other end 'of resistance 2| is connected to a-movable switchcontact 22. A stationary contact 24 .of said switch is connected to theend negative pole of a plurality of "dry cells 25 in series as shown byconductor 26. The end positive pole of said dry cells 25 is connected toconductor 22 by conductor 21. A movable contact 28 has its stationaryend connected to conductor it and its-free or movable end may be movedalong the resistance 2| and therewith comprises a p0tentiometer. A threeelectrode vacuum tube includingan anode 2|, cathode 3| and grid 22 hasits grid 32 connected to conductor [9 by conductor 32. One side ofcathode 3| is connected to the stationary switch contact 34 and itsother end connected to the end positive pole of a plurality of dry cells35 in series. A conductor 35 connects the end negative pole of dry cellsto a movable contact 31 of said switch. .A standard dry cell 38 of 1.5v. has its negative pole connected to the conductor l8 by conductor 3,0and ammeter 4| has one end connected to anode by A conductor 42 and itsother end connected to the end positive pole of dry cells 43 in seriesby conconductor 40 is the stationary contact 5| oi a switch whosemovable contact 52 is connected to one end of a resistance 53 byconductor 54. The other end of resistance 53 is connected by conductor55 to a movable contact 5601' a switch whose stationary contact 51 isconnected by conductor 58 to a contact 59 of another switch. The contact59; is connected to conductor 46 by conductor 60. A contact Si islocated below contact 59 and is connected to one end of a resistance 62by conductor 63. The other end of resistance 62 is connected toconductor 54 by conductor 64. A galvanometer 65 has one terminalconnected to conductor 64 by conductor 66. A contact ("is connected tomember 55 by conductor 68 and the other terminal of galvanometer 65 isconnected to conductor'tt by conductor 69. A movable T switch contact I0has one end permanently connected to contact 61 and the cross barthereof is normally located above and out of contact with contacts 59and BI. Located in front of the photoelectric cellis a source of lightand for this purpose, I prefer to employ a well known zinc vapor lamp,which produces six strong lines between 3282 Angstrom units and 3346Angstrom units, some lines at and below 3076 Angstrom units and somestrong lines 55 between the source of light and the photocell ordertoabsorb the 3076 line and any there-' below aswell as those in thevisible portion of the spectrum to which the cell is sensitive, butallows the passing therethrough of the six strong lines between 3282 and3346 Angstrom units. For this light 90 maybe located a shutter 94adapted to be opened and closed by rod 95 having one end secured tomovable switch contact 23.

The following is an explanation of the func-''' tioning'of the parts andthe operation. of the -i circuit as shown and described. Contact 31 maybe moved to closed position on contact 34 to complete the heatingcircuit for cathode 3|.sothat .cathode 3| may be in electron emissivecondition, and contact l4 may be moved to closed position on contact l6to complete the main photoelectric circuit. ,other switches open asshown, the grid 32 is 1.5 v. or A egative than the cathode 3| due tothel.5 en '38 and the photoelectric cell is not enerized'. At thisstageit will be noted that the mmeter reading may be .100 ma.

The'jcell 93 is removed from between the filter '9 "and"'shutter 94. Thezinc vapor lamp 90 is energized by"a suitable source of E. M. F. andmovable contact 23is actuated to closed position on.' contact 24 andsimultaneously to actuate rod 7 95 whereupon shutter 94 is opened.

Theswitch contact 52 ismoved to closed position on contact 5|. The lightfrom the lamp 99 strikes cathode I and energizes the same, whereuponthere is an IR. drop across the high re- With this condition existingand thethis condition a galvanometer ,thereacross will read 0. 1

In order to protect the galvanometer 65, the resistance 62 is employed.Since the resistance of galvanometer 65 is about 1000 ohms, it ispreferred that the rough adjustment resistance 62 be about 50 ohms andthe critical damping resistance 53 may be 1000 ohms. In operation afterthe resistance 45 has been varied the 1' contact 10 is pressed down to.connect contacts 59, 6| and 61 to eachother whereupon most of thecurrent passes through shunt resistance 62 and the galvanometerdeflection is noted wheresimple manner.

' solvent therein, the shutter 94 is in closed position and the lamp 90is energized, switch consistance 20 and .an IR drop across theresistance 2|. negligible because resistance 2| is of the order of 100ohms, when compared with the IR drop across resistance 20. The IR dropacross resistance" tends to make the grid more negative, but the 1R dropacross 2| due to 23 being closed tends to make the grid more positiveand the ultimate potential relationship between grid 32 and cathode 3|will be reflected in the reading of ammeter 4| which is now observed.Ordinarily this reading will be at variance with the first noted reading01. .100ma. The ositions of the movable end 29 oi conductor 29along theresistance 2| may be varied until the IR. drop across the resistance 20and the 1R drop of the resistance 2| from its upper limit to the end 29is equal and opposite so that the grid 32 is exactly 1.5 v. negative tothe cathode and the meter reads as before .100 ma.

Since the vapor lamp 90 is energized by an alternating current source ofelectric energy, the

I The potential'of the conductor 49 just below "the negative pole ofbatteryll is more negative than the lowermost part of resistance byvirtue of battery 41 and the variable resistance is ad- 'iusted so thatthe IR drop through resistance 45 equal to the potential of battery-41and under The IR. drop across the resistance 2|- is- I uponthevresistance 45 is varied until the galvanometer reads 0. Then the contact10 is released to disconnect contacts 59, 6| and 61 from each othe'randcontact 56 is closed down on contact 51 and the galvanometer deflectionis again noted and the resistance 45 is further varied until thegalvanometer now reads 0.

Assuming that the parts described are ar-' ranged as set forth hereinand shown in the drawing, the concentration of a vitamin A solution orthe like-may be measured rapidly and exactly by an unskilledoperator inthe following The cell 93 now contains only tacts I4, 31 and 52 areactuated to closed positions. After about 5 minutes, contact 10 isactuated to closed position and the variableresistance 45 is varieduntil galvanometer 65 reads 0 whereupon contact I0 is released andcontact 56 is actuated to closed position and if the galvanometer doesnot read 0, resistance 45 is further varied until it does and releasescontact 56. I

Then actuate switch contact 23 to closedposition whereupon rod 95 isactuated to open shutter 94. Actuate contact HI-to clomd position andthen adjust resistance 2 I by moving contact 29 The cell containing thissolution is placed in the same position as was that cell containingonly.

the solvent. The galvanometer circuit is balanced as before by movingcontact 10 to closed position by varying resistance 45 until the gal-'vanometer reads 0, releasing contact 10 and actuating contact 56 toclosed position and if necessary, varying resistance 45 untilgalvanometer reads 0 and releasing contact 56.

- Switch contact 234s actuatedv to move contact 23 to closedposition"and sirnultaneously'to open shutter 94. The light fromlamppasses successively through shutter 94, cell 93 plus the solutiontherein and fllter to the cathode ll of the photoelectric cell. Thecontact 10 is moved to closed position and the contact 29 is moved alongresistance 2| until ,the galvanometer reads 0.

Then'contact I0 is released and contact 56 is.

moved to closed position and, if necessary, contact 29 is moved furtheralong resistance 2| until the galvanometer again reads 0 and contact 56is now released. The potentiometer reading at 2| is now taken and notedas Par All .closed switches may now be opened until it is time for thenext sample to be tested,

Since the potentiometer readings P1 and P2 arev directly'proportional tothe photocell current, which is in turn, proportional to the lightaflfecting the photocell, from these two readings may be readilycalculated the E value in the customary manner.

Although the inventiorrhas been described with minute particularity, itis not to be limited thereby, because various changes'may be made withinthe scope of the invention. What is claimed: 1. Apparatus for measuringthe concentration of vitamin A in a substance comprising a zinc vaporsource of light, photoelectric means upon which the light from saidsource is directed, said photoelectric means being substantiallyinsensitive to those lines above 5000 Angstrom units in the visiblespectrum, a filter located between said source of light and saidphotoelectric means, said filter adapted to absorb substantially allradiation except those between 3282 and 3346 Augstrom units, to whichsaid means is sensitive, means for interposing a sample of substance to-,be measured between said source of light and said photoelectric meansand means connected to said photoelectric means vfor indicating thedegree of change in photoelectric current.

2. Apparatus for measuring the concentration oi vitamin A in a substancecomprising a zinc vapor source of light, a circuit comprising aphotoelectric cell including an-anode and cathode, said cathode composedof sodium, a source tiometer, a second circuit including a source ofelectric energy, and a three electrode vacuum tube including anode,cathode and grid, and

means for indicating the plate current at said anode, said gridconnected to said first fcircuit.

3. Apparatus for measuring the concentration of vitamin A in a substancecomprising a zinc ,vapor source of light, a photoelectric cell includingan anode and a sodium surface cathode, saidcell located in the path oflight from said source of light, a filter adapted to absorb allradiation to be measured and a shutter adapted to be opened and closed,said shutter located between saidsource of light and said means.

4. Apparatus for measuring the concentration of vitamin A in a substancecomprising a zinc vapor source of light, a photoelectric cell ineludingan anode and a sodium surface cathode, said cell located in the path oflight from said source, a liter adapted to absorb the lightfromsaidsource below 3076 Angstrom units, 'said filter interposed betweensaid source of light and said cell, means for interposing between saidfilter measured, a circuit including a source of electric energy, saidcell, a high'resistor and a potentiof electric energy, a high resistanceand poten- 85 ometer, a three electrode amplifying tube. the grid ofsaid tube connected to the anode of said cell, the cathode of said tubeconnected to said potentiometer and means connected to the anode of saidtube for indicating the plate current,

BEAUMONT nnmnns'n'

